Endless power transmission belts having a socalled central neutral axis (CNA) i.e., load-carrying means such as helically wound load-carrying cord disposed midway between the outside and inside surfaces of the belt, are becoming more popular in the belt industry due to their inherent capability of being produced with minimum scrap.
It is common practice in a CNA belt as well as a more conventional belt to employ layers of polymer impregnated fabric at various locations throughout the belt cross section. However, during the operation of such belts around associated sheaves there is repeated flexing and imposition of stresses thereon and particularly on the fabric plies as each belt enters and exits each associated sheave and the stresses on fabric plies is aggravated when employing sheaves of comparatively small diameter. The fabric layers of such belts are usually made of fibers which are comparatively rigid and inelastic and when loading such fibers they and their associated fabric tend to fail prematurely causing premature belt failure.
Heretofore, it was well known that the more conventional belts, i.e., those having their neutral axis close to the outside surface of the belt, performed better if such belts were kept comparatively thin when measured perpendicular to their parallel sides. However, in the course of CNA belt development it was found that certain thicker CNA belts gave better performance which led to this invention. In particular it was found that there is an optimum amount of polymeric material that can be disposed against greige fabric to provide improved performance without belt delamination.